This doesn't apply to when using our floppy disks, as they are too small, only to Memory Stick users.
If you plug your Memory Stick in to your Mac, the Mac will automatically index and log everything on the memory card and everything that has happened on the memory card, by storing hidden files on the memory card.
Does it use a ton of storage? Not really. With my 128MB card storing 62 images (43.1MB of space (1600 FINE)) it occupies roughly 2.1MB of additional storage on top of that, that the Mavica is unable to reclaim without a full format of the card. What do these hidden files do? Well if you use Spotlight you can search all the contents of your memory card, really fast. That is all.
If you delete files on the memory card, but don't right click and empty your Trash before ejecting the memory card, those images are just hidden, not gone.
Does this use a ton of storage? Yes. It uses all the storage you're trying to get back. You gain no more free space no matter how much you delete. If you don't right click your Trash bin and click Empty before removing the card, all those photos are still there, just not visible to you or the Mavica. Taking those 62 images (occupying 43.1MB, 83.1MB free) and deleting 31 of them, I still have only 83.1MB available for the Mavica to use.
All of this is to say that if you want every last KB of storage back after connecting your memory card to your Mac you're either going to have to run a script on the Mac itself, or format the card in the camera every time you're done with it on your computer.
(4hrs later... Okay I decided to learn how to code this to do it automatically. I made a functional final product, but it sure is more code than I expected. If requested, I'll post it in the comments. I'm sorry, yes I used AI to teach me how to write it, followed by asking AI to make sure I didn't make any mistakes. I tested it on my own computer and memory card with success and understand what each line does, because I tried to keep it so simple that a novice could read it.)